1. Field of the Invention
The present invention relates to a plasma display panel. More particularly, the present invention relates to a plasma display panel that includes a front substrate, a rear substrate and Intermediate barrier ribs defining a discharge cells and having sustain electrodes located therein, in which a space between the front substrate and the rear substrate can be divided into an emissive area having a fluorescent layer and a non-emissive area around the emissive area, the non-emissive area having an epoxy molding compound sealing the space of the emissive area from the outside, thus improving the sealing efficiency of the plasma display panel.
2. Description of the Prior Art
As generally known in the art, a plasma display panel refers to a panel used in a plasma display device, which is a kind of flat display device that realizes an image from a visible ray emitted from a fluorescent layer when the fluorescent layer is excited by ultraviolet rays. The ultraviolet rays are produced by a plasma created when a gas discharge is produced in a discharge gas filling a space between two opposite substrates. Such a plasma display panel can be classified into a DC type plasma display panel, an AC type plasma display panel and an AC-DC type plasma display panel according to the structure and the driving principle thereof. In addition, the plasma display panel can be classified into a surface discharge type plasma display panel and an opposed type plasma display panel according to the discharge structure thereof. Recently, AC-type three-electrode surface discharge plasma panels have been extensively used.
A plasma display panel generally includes a front substrate, a rear substrate opposing the front substrate, and an electrode required for the discharge operation. The front substrate is a glass substrate having a thickness of about 2.8 mm and is made out of a transparent soda glass such that a visible rays produced in the fluorescent layer may pass therethrough. A pair of X-Y electrodes are provided at a lower surface of the front substrate in order to generate a sustain discharge. Such electrodes include a transparent electrode that can be made out of ITO (Indium Tin Oxide). A bus electrode is formed at a lower portion of the transparent electrode. The bus electrode has a width smaller than that of the transparent electrode and compensates for line resistance of the transparent electrode. The front substrate is provided at the lower surface thereof with a dielectric layer in order to cover the transparent electrodes therein so that the transparent electrodes are prevented from being exposed. In addition, a passivation layer is formed on the dielectric layer in order to protect the dielectric layer.
On an upper surface of the rear substrate are address electrodes that are alternately located with the transparent electrodes formed on the lower surface of the front substrate. In addition, similar to the front substrate, a dielectric layer covers the address electrodes to prevent the address electrodes formed on the upper surface of the rear substrate from being exposed. Barrier ribs are formed on the upper surface of the rear substrate so as to prevent electro-optical cross-talk between neighboring discharge cells while maintaining a discharge distance. The barrier ribs are provided between the front and the rear substrates to form spaces for generating the plasma discharge and to define discharge cells. The discharge cells are elements of pixels serving as basic units for displaying an image in a plasma display panel. Red, green and blue fluorescent layers are coated on both sidewalls of the barrier ribs that define the discharge cells as well as on portions of the upper surface of the dielectric layer of the rear substrate where the barrier ribs are not present.
The plasma display panel having the above structure adjusts the number of sustain discharge operations according to video data transmitted thereto, thus achieving a gray scale required for displaying an image. In order to represent the gray scale, an ADS (address and display period separated) scheme is used where one frame is driven while being divided into a plurality of sub-fields having different numbers of discharging operations. According to the ADS scheme, each sub-field is divided into a reset period for uniformly generating the discharge, an address period for selecting a discharge cell and sustain and erase periods for expressing the gray scale according to the number of the discharge operations.
During the address period of the sub-field, an address discharge is generated due to a difference between an address voltage applied to an address electrode located at a lower portion of a selected discharge cell causing the discharge to be produced and causing a ground voltage to be applied to a scan electrode (Y electrode). In addition, although an address voltage with straight polarity is applied to the address electrodes located at the lower portion of the selected discharge cell, a ground voltage is applied to other, non-selected address electrodes. Therefore, if a display data signal of the address voltage having the straight polarity is applied while a scan pulse of the ground voltage is being applied, a wall charge is formed in the corresponding discharge cells due to the address discharge, but the wall charge is not formed in the other, non-selected discharge cells. The sustain electrode (X electrode) is maintained with a predetermined voltage for effectively generating the address discharge during the address period. Intensity of the address voltage required for the address discharge may exert influence upon optical efficiency, structure and materials in the display panel. Specifically, as the intensity of the address voltage rises, power consumption may increase, so that the optical efficiency is reduced. This is caused by a sputtering effect that is increasingly generated in the dielectric layers of the rear and front substrates, causing the number of charged particles moving into adjacent discharge cells through the barrier ribs to increase (that is, the cross-talk may increase). Therefore, typically, it is advantageous to keep the address firing voltage low.
However, according to the three-electrode type surface discharge scheme, since a distance between the scan electrode and the address electrode is small, a relatively large discharge voltage is required. In addition, the discharge starts at an area in which a distance between two electrodes is smallest (i.e., at a center area of a discharge cell). After initiation, the discharge is produced at a peripheral area of the electrodes. That is, when a low firing voltage is applied to the center of the discharge cell, the discharge is produced in the center of the discharge cell. Once the discharge is initiated, space charges are generated so that the discharge operation can be maintained at a voltage that is lower than the firing voltage, allowing for the voltage applied between two electrodes to be gradually reduced as time goes by. As the discharge operation starts, ions and electrons are accumulated in the center of the discharge cell so that the intensity of an electric field in the center of the discharge cell can be reduced so that the discharge in the center of the discharge cell can vanish. That is, since the voltage applied between two electrodes reduces with time, a strong discharge may occur at the center of the discharge cell having a low light efficiency and a weak discharge may occur at the peripheral portion of the discharge cell having a high light efficiency. In such a scenario, the plasma display panel employing the three-electrode type surface discharge scheme uses a relatively lower amount of input energy for heating electrons, so that the light efficiency of the plasma display panel can be degraded.
Recently, in order to solve the problem occurring in the plasma display panel employing the above three-electrode type surface discharge scheme, a plasma display panel employing an opposed discharge scheme has been developed. According to the opposed discharge scheme, an X electrode and a Y electrode are formed in intermediate barrier ribs and oppose each other at a space formed between a front substrate and a rear substrate. Address electrodes are located alternately with the X and Y electrodes in the vertical direction. Therefore, according to the plasma display panel employing the opposed discharge scheme, a distance between a scan electrode and an address electrode is smaller than a distance between the scan electrode and the address electrode of the plasma display panel employing the surface discharge scheme, so that the address voltage is relatively lower. In addition, according to the opposed discharge scheme, the plasma discharge is generated over the whole area of the discharge cell so that a discharge space is enlarged, thus increasing the discharge efficiency. In the meantime, according to the opposed discharge scheme, the discharge space formed between the front substrate and the rear substrate must be sealed. If the sealing efficiency is degraded, discharge gas can leak or the light emitting efficiency can be lowered, thus degrading the brightness of the panel.
However, in the plasma display panel employing the opposed discharge scheme, it is difficult to effectively seal the discharge space formed between the front substrate and the rear substrate as compared with the plasma display panel employing the surface discharge scheme. In particular, if the plasma display panel is fabricated with intermediate barrier ribs separately formed between the front substrate and the rear substrate to define the discharge cells, it is necessary to simultaneously seal gaps formed between the front substrate and the intermediate barrier ribs as well as between the rear substrate and the intermediate barrier ribs, respectively, so that the sealing efficiency may be degraded. Therefore, what is needed is an improved design for an opposed discharge scheme plasma display panel.